This application describes a wide-ranging integrated program of research directed toward an understanding of the behavioral characteristics, developmental course, neural processing, neuropathology, and genetics of autism. The central organizing theme of our program is a focus on language. Since Kanner first described autism over fifty years ago, it has clearly been recognized that language impairments are primary features of the syndrome. It is a key prognostic factor that predicts levels of functioning across all other domains. Furthermore, language related deficits are among the main characteristics of the broader autism phenotype seen in family members, as a manifestation of the genetic liability to. Because language is so central to the syndrome, we have selected this domain as the focus of our multidiscriplinary approach for this program project. The research proposed here will address questions about: Project I: the developmental course of the cores areas of behavioral impairment (language and social functioning): Project II: the behavioral phenotype in severely affected individuals; Project III: how the brains of autistic individuals process language and structural characteristics of autistic brains in language regions. Our aims are to study each of these levels of analysis simultaneously in overlapping groups of autistic individuals and matched controls who span a wide range of age, level of functioning, and intellectual impairment, and whom we plan to follow longitudinally, in a cohort sequential design. The program will be supported by a unified Clinical and Administrative Core whose major functions will be to recruit subjects for the major clinical projects, provide diagnostic, psychiatric, neuropsychological and clinical dysmorphology evaluations of the participants in the project, and provide data management and statistical support to each component project and the overall program.